Sanding device



F". A. DOBSON SANDING DEVICE Aug. s, 195o 3 Sheets-Sheet 2 Filed July 26, 1947 1 .\\\\Allilllillallllllllllll|1154n 4 Qu @u Nk f? 7' TOE/VE YS,

fam -f Patented Aug. 8, 1950 UNITED STATES PATENT OFFICE SANDING DEVICE Franklin A. Dobson, Royal Oak, Mich. Application July 26, 1947, Serial No. 763,769

16 Claiml. (Cl. 51-170l This invention relates to a sanding machine and more particularly to a portable and manually operable machine which is adapted to be manipulated over a surface to remove irregularities and produce a smooth nish.

Sanders of this type usually employ a motor driven reciprocating pad to which a suitable abrasive, usually in sheet form. is secured to produce the desired finish. I have found that for best results a sanding machine of this type should be small, compact and light. The machine must be free from vibration and should have a well cushioned pad capable of producing a straight back and forth sanding Ipattern. Unless the machine is small and compact it is unsuitable for work in close and limited space and a machine which is heavy and bulky not only tires the operator but makes accurate work dimcult. The same is true of vibration. Sanders which vibrate excessively are not only unpleasant to handle but also prevent obtaining a perfect finish. In addition, the vibration consumes a large portion. of the power supplied by the motor which would otherwise be utilized by the pad in performing work. Vibration also prevents a rapid cutting action because when pressure is applied to unbalanced sanders it merely accentuates the vibrating movement of the frame While the pad itself remains stationary. With some types of work the vibration and the sanding pattern do not appreciably effect the finish obtained. but to produce an extremely iine finish on wood, for example, these factors are of the utmost importance. Unless the pad is well cushioned the abrasive will dig into the work instead of sanding it uniformly and if the -pad moves in other than a straight line path parallel to the grain of the wood. cross-grain scratches, and consequently an imperfect flnish. are inevitable. h

One of the objects of this invention is to provide a sander which is small, compact and light and therefore convenient and easy to handle.

Another object of the invention resides in the provision of novel means for balancing the reciprocating weight of the sander to completely eliminate the vibration transmitted to the hand of the operator. the means employed being especially suitable for this purpose since no additional moving parts are required other than those normally required to suspend the pad on the frame of the sander.

A further object of this invention is to provide Y means for suspending the pad on the frame of the sander in a manner which produces a straight Another object is to provide a machine of this type which is easy to assemble and disassemble and the parts of which do not have to be machined to close tolerance and therefore enable their economical manufacture.

Further objects in the way of construction and operation will become evident by the following description and drawings in which:

Figure 1 is a side elevation, partly in section, oi a sanding machine embodying the principles of my invention.

Figure 2 is an end elevationI partly in section, of the machine shown in Figure 1,

Figure 3 is a sectional view taken along line 3-3 in Figure 1.

Figure 4 is a sectional view taken along line 4--4 of Figure 1 illustrating the manner in which the pad is secured to the reciprocating carriage.

Figure 5 is a partial sectional view of one end of the sander showing a modified construction which may be utilized to restrict the movement of the pad to a single horizontal plane.

Figure 6 is a perspective view of a modified form of carriage construction in which the counterweight assembly is an integral part of the carriage itself.

Figure 7 is a sectional view taken substantially along line 1-1 in Figure 6.

Figure 8 is a sectional view taken substantially along line 8-8 in Figure 6.

Figure 9 is a diagrammatic view of the reciprocating elements together with a representation of the forces resulting from a particular movement of the pad.

Figure 10 is a force vector diagram of the forces illustrated in Figure 9.

Figure 11 is a diagrammatic view of the pad and rocker arm assembly with the lengths of various elements of the assembly suitably indicated.

Referring to the drawings and particularly to Figure 1, there is shown a motor I0 mounted in a frame I2 with its shaft I4 extending vertically downwardly and journaled within bearing I6 in the frame. At the rear end of the frame there is provided a handle I8 having a switch 20 located at its upper end and readily accessible by the thumb of the operator. The handle I8 curves upwardly and forwardly so that it may be conveniently gripped for sanding in either a vertical or a horizontal plane. Suitable conductors, not shown, connect the motor III with switch 20 and emerge from the lower end of handle I8 for connection with a source of electric power. At the front end of the frame a handle 22 in the form of a knob is threadedly engaged with the frame A freely rotatable connection is provided therebetween by means of a sealed ball-bearing 28. The other end of connecting rod 26 is pivotally secured to a carriage 30 by means of a rubber bushing l2. In order to'protect the eccentric bearing as much as possible from misalignment it is preferred that connecting rod 26 be exible and accordingly I prefer to utilize a connecting rod comprising two sections 34 and 36 which are joined by a ilexible leaf spring l0. Misalignment of the eccentric bearing can also be prevented by using a selfaligning bearing, a bearing mounted in rubber or a properly designed connecting rod of flexible material.

The carriage 30 comprises a rectangular frame having a pair of side members 40 and 42 which are pivotally connected to the frame I2 by means of rocker arms 44 so as to provide a parallelogram linkage between the carriage and the frame. The side members 40 and 42 are provided with transverse rubber bushings 46 press fitted into the ends thereof. As is best shown in Figure 2, a tubular spacer 48 extends between the bushings 46 at each end of the carriage, and rocker arms 44 are clamped against the bushings by means of a nut and bolt arrangement 50. In like manner, rocker arms 44 are plvotally attached to the frame I2 by means of rubber bushings 54 press iitted into the frame as at 55. The rocker arms are clamped between bushings 54 and a tubular spacer 58 by means of a nut and bolt arrangement 60. It will be observed that the parallelogram linkage which -I have provided between the carriage and the frame, prevents lateral movement oi.' the carriage with respect to the frame and results in a straight back and forth movement of the carriage. At the same time any movement of rocker arms 44 takes place by means of shear in rubber bushings 46 and 54 rather than by any sliding action between these parts. The carriage 30 is secured to a sander plate 52 by means of two pairs of :flexible leaf springs 64 which extend across and are secured to the side members 40 and 42 as at 52. The leaf springs 64 in each pair are secured together at their midpoint by means of a stud 06 which passes through' the inner spacer sleeve 60 of bushings 32. The lower end of stud 56 is provided with a ball-shaped head 10 which is adapted to seat in a cooperating slotted socket 12 which is formed ln plate 02. The head 10 of stud 66 is removably retained in socket 'I2 by means of a spring 14 acting between the peened lower end 1l of the stud and a retaining washer 15 which abuts against the lower lace of plate 62. The slotted sockets 12 are provided with enlarged openings 10 at one end thereof which permit the passage therethrough of retaining washers 1l. The sander plate may be removed from the carriage by rotating it to a position which permits withdrawing retaining washers 10 through the enlarged openings 10. A resilient pad l is secured to the' bottom face of plate 62 and an abrasive 02 is cemented to pad 80 by means of a tacky adhesive which permits the abrasive to be removed and replaced at will.

It will be seen that springs 64 provide a positive driving connection between plate 62 and carriage 30 and at the same time vertically cushion the plate l2. Freedom of vertical movement of plate 02 is necessary since the foreshortening of rocker arms 44 which results from their reciprodesired by resilient pads 04 as shown in Figure 4 which may be arranged to produce any desired degree of freedom between the carriage 3l and the plate 62.

In Figure 5 there is shown another method oi' cushioning plate 62 so as to insure its movement in a single horizontal plane. Auxiliary rocker arms |02 are secured to rocker arms 44 and have their lower ends bearingupon pads |04 which are secured to plate 02. 'Ihe bearing surface |08 of arms |02 is cylindrical in shape, the center 'of the cylinder being the axis of bushings I4. 'Ihis arrangement results in perfect linear movement with no sliding between the arms |02 and pads |04. At the same time, since the distance between the axes of bushings 54 and the contact point on bearing surface |06 is constant, springs G4 flex upon movement of rocker arms 44 and plte 52 reciprccates in a perfectly horizontal p ne.

The upper ends of rocker arms 44 are inclined inwardly towards the center of the sander and support cylindrical balance weights 0l. These weights are arranged to entirely eliminate vibration in the sander due to the reciprocating weight of the carriage and pad assembly and the arrangement by which this is accomplished will now be explained. Assuming that the pad has an acceleration to the left as shown by the arrow 00 in Figure 9. balance weights Il are accelerated in the directions shown by arrows 00 and '02. At the same time, acceleration of the pad and carriage assembly exerts an inertia force $4 on the frame I2 in an opposite direction and passing through its center oi' gravity. Likewise, inertia forces and 00 result from the acceleration of balance weights 00. By simple calculations the 'angular inclination of theupper portion oi' arms 44 may be determined so that inertia forces 04 and 00 of balance weights l0 intersect at approximately the center of gravity of the pad and carrlage assembly. In Figure 10 I have shown the inertia forces of the balance weights in the form of a vector diagram and lt will be seen therefrom that the resultant of these forces is their vector sum |00. a horizontal force acting in a direction opposite to the direction of the ineria force 04 of the pad and carriage assembly. Since, as described above, forces 06 and 00 intersect-at the center oi gravity of the pad and carriage assembly, their resultant force |00 also through this point. By means of the vectordlagram the masses of weights 08 can be calculated so that their resultant inertia forces. exactly equal to the inertia forces of the pad and riage assembly. This results in an arrangement in which equal and opposite forces act along the same path and thereby eliminate all vibration due to the reclprocating'm'ovement of the pad and carriage assembly.

In the above explanation the assumption is made that the masses of balance weights 00 concentrated at their respective centers of gravity and that rocker arms 44 have no weight. likewise, the centrifugal force due to the rotationb the arms 44 about their axes has not been taken into account. I have found'that asa matter of practical design these corrections may be disregarded since arms 44 only move through angles up to l2 or 15 degrees and in this range 'f corrections are very small.

The masses of weights 06 and the angular inclinatlon ofthe rocker arms may be calculated with even greater accuracy than the vector method by means of algebraic equations derived by balancing the horizontal forces and the moments of inertia. For a symmetrical design l auch as is shown in Figure 11 with the pad in the center position, the following equations may be used to calculate these values:

In the above equations c represents the weight of one rocker arm assembly including the balance weight I6. W-represents the weight of all reciprocating parts of the pad assembly and the point W, the center of gravity of the reciprocating pad assembly. r represents the lever arm between the pad and frame and h and s, the vertical and horizontal components respectively of the balance weight lever arm. a represents the distance between the pivot points on the pad assembly and d, the vertical distance between the rocker arm pivot points on the frame and the center of gravity of the pad assembly. ly is the radius of gyration of the rocker arm assembly about its center of gravity. In most instances the quantities a, r, d, h, W. and y are fixed by the physical limitations of the design and the quantities c and s may be calculated to give perfect balance. The value of s as determined by the above equation is slightly greater than that obtained by the vector method, in which method it is assumed that y is equal to zero.

Vibration due to rotation of eccentric 2l is, of course. independent of the vibration due to reciprocation and this is eliminated by an olf-set counter weight |02 which is secured to the motor shaft i4 and proportioned such that it exactly balances the inertia force of eccentric 2l, bearing 20 and end 34 of connecting rod 26.

In Figure 6 there is shown a modified construction of the sander employing the same principle of balancing weights as previously described but with less moving parts. In this form of sander the rocker arms |08 are made integral with transverse springs which deflect torsionally with the pivotal movement of the rocker arms. Rigid spacers ||2 are secured to the springs ||0 at their midpoints and are provided with threaded studs lil for attaching the pad plate H6 and pad (not shown) to rocker arms |00. At the lower end of rocker arms |00, where they bend to form transverse springs IIO. the bend is made so that the lower surface of springs lill is cylindrical in shape with its center at the axis of pivoting of the rocker arms. These surfaces, indicated as iiB, are supported by resilient pads on the sander plate |I6. will be observed that this arrangement results in straight line motion of plate iii as previously described with reference to the structure shown in Figure 5.

In order to form the cylindrical surface on springs ||0 without unduly stretching the metal at the bend, the adjacent vertical portion of the rocker arm is formed to an equal and opposite curvature. I have found that this curvature not only produces a better bend but also reinforces the rocker arm and resists lateral flexing of the arm.

I have also determined that best performance is attained when the end surfaces lili are maintained snugly against pads |20. Tension springs |22 backed at one end to the rocker arm bolts |24 and at the other end to blocks |26 fixed to springs ||0 may be employed for this purpose.

Itl

In this form of sander there is also shown a modified construction for the connecting rod which, as shown. comprises a vertically disposed leaf spring 2|! clamped at one end to one of the blocks |28 and having `a yoke |30 secured to its other end. The other end of yoke |30 is attached to the ends of a horizontally disposed leaf spring |32 which is carried by the bearing collar |24.

Although I have shown a direct drive between the motor and the pad, it will be appreciated that the type of drive employed will depend to a large extent upon the motor characteristics. With some types of motors speed reducing means, such as gearing, would have to be employed, but the invention is equally adapted to that type of arrangement since the reciprocating weight can be balanced in the same manner as described.

It will thus be seen that I have provided a simply constructed sanding machine which is adapted to produce an extremely fine finish on all types of work surfaces. The rocker arm linkage provided between the carriage and frame of the sander possesses distinct advantages over arrangements employed on other sanding machines with which I am familiar. It produces a straight back and forth sanding pattern without the use of racks, guides and numerous other parts and at the same time provides means for balancing the reciprocating weight of the sander in a novel and efficient manner. By employing rubber bushings as described. the necessity for lubricating the sander is eliminated and since frictional losses are reduced a motor of slower speed than commonly used may be employed.

I claim:

1. In a sanding machine, a frame, a sander plate, a motor mounted on said frame and operatively connected with said plate for reciprocating said plate, a plurality of rigid links pivoted on said frame for pivotal movement in a plane longitudinally of said frame, means operatively connecting said plate with said links below said frame so that said links oscillate when said plate is reciprocated, and means on each of said links having a cylindrical surface spaced a fixed distance from the pivotal connection between said links and said frame contacting bearing surfaces on said plate such that said plate oscillates in a single horizontal plane below said frame.

2. In a sanding machine, a frame, a. motor mounted on said frame, a pad assembly., a plurality of rocker arms pivoted on said frame and suspending said pad assembly below said frame, said rocker arms being arranged to prevent movement of said pad assembly laterally of saldi frame. eccentric means operatively connecting said motor and pad assembly for reciprocating said pad assembly longitudinally of said frame, means on said pad assembly forming horizontal bearing surfaces on said pad assembly, and means on said rocker arms having cylindrical surfaces in bearing contact with said bearing surfaces, said last mentioned means being disposed such that radii of said cylindrical surfaces pass through the pivotal connection between said rocker arms and said frame whereby said pad assembly is oscillated in a single horizontal Diane and along a path longitudinally of said frame.

3. In a sanding machine having a frame and a pad assembly suspended from said frame and arranged to oscillate longitudinally of said frame, means for balancing the inertia force exerted by said oscillating pad assembly on said frame comprising means for applying an inertia force in substantially in the path of the inertia force of A said pad assembly and so that the resultant ot said first and second inertia forces is substantllly equal and opposite in direction to the inertia torce of said pad.

4. In a sanding machine having a irame and a pad assembly suspended from said irame and arranged to oscillate longitudinally oi said frame, means for balancing the inertia force exerted by said oscillating pad assembly on said frame comprising reciprocating means on said frame for applying a plurality of inertia forces to said frame acting in dilerent directions which intersect at a point substantially in the path of travel of the center of gravity of said oscillating pad assembly, said reciprocating means -being arranged so that the resultant of the inertia forces applied by said means is substantially equal and opposite in direction to the inertia force of said reciprocating pad assembly.

5. In a sander having a frame and a pad assembly suspended from said frame and arranged tov'oscillate longitudinally of said frame, means for" balancing the inertia force exerted by said oscillating pad assembly on said frame comprising a pair of balance weights, means on'said frame for reciprocating said weights in diierent directions longitudinally of said frame, said means being arranged so that the paths of the inertia forces of said reciprocating weights intersect at a point in a plant substantially parallel to the'plane of said reciprocating pad assembly` and in which the inertia force of said oscillating pad assembly acts and so that the resultant force of the inertia forces of said balance weights is substantially equal and opposite in direction to the inertia force of said pad assembly.

6. In a sanding machine having a frame and a pad assembly suspended from said frame and arranged to oscillate longitudinally of said frame, means lor balancing the inertia force exerted by said oscillating pad assembly on said frame com'- pri'sing 'a plurality of balance weights. rocker arms pivoted on said frame and arranged to oscillate said weights in different directions along paths inclined to the path of said oscillating pad assembly, said rocker arms being actuated at the same speed as said oscillating pad assembly, said rocker arms being arranged to oscillate said balance weights such that the paths of the inertia forces of said weights intersect at a point substantially in the path of the inertia force ot said pad assembly.

'1. A sanding device comprising a frame, a plurality of rocker arms pivoted between their ends on said frame for pivotal movement in a plane longitudinally of said frame, a pad assembly, means operatively connecting said pad assembly to the lower ends of said rocker arms, means on said frame for reciprocating said pad assembly along a path longitudinally of said frame and balance weights on the upper ends of said' rocker arms. the upper portions of said rocker arms being inclined towards the center of said frame so that the inertia forces of said weights act in paths which intersect substantially at a point through which the inertia force of said pad assembly acts.

8. A sanding device comprising a frame, a plurality of rocker arms pivoted on said frame at frame. a pad assembly operatively to, the lower ends of said rocker arms. xneans on said frame for oscillating said rocker arms and pad assembly. and balance weights at opposite ends oi said' frame oscillated by the upper ends of said rocker arms' in a path such that the resultant of the inertia forces oi said weights acts in substantially the same path but in opposite directions as the inertia force oi said pad assembly.

9. The combination as set forth in claim 8 wherein lsaid weights have masses such that the resultant of the inertia forces of said weights is substantially equal to the inertia force oi said pad assembly.

10. In a sanding device, a frame. a pad assembly means suspending said pad assembly below said frame so as to be reciprocable along a path longitudinally of said frame, a plurality of balance weights reciprocably mounted on said frame. and means for reciprocating said pad as sembly and simultaneously reciprocating some of said balance weights in one direction and others ui'V said weights ina direction inclined to said 'first direction so that the resultant oi-the inertia forces ot said reciprocating -weights acts in substantially the same path but opposite in direction to the path of the inertia force oi said reciprocating pad assembly.

11 Ina sanding device, a frame, a pad assembly,'means =suspending said pad assembly from and `belbvvsaid frame comprising a plurality oi links eachl having an upwardly extending leg and an integral horizontally extending leg at 4the lowerjend loi said upright leg. said upright leg beingfpi'voted on said frame and said horizontal leg being rigidly connected at a point intermedi-- ateV ttsends' with said pad assembly,"and means for reciprocating said pad Vlongitudinally oi' said frame. said horizontal leg being torsionally dis'- tortable so as to permit said upright leg to pivot relative' to said pad assembly when the pad assembly-'is reciprocated.

l2. In a sanding device, a frame, a pad as-v ally when said pad assembly is reciprocated.

13. A device comprising a frame, a plurality of links pivoted intermediate their ends on said frame for movement in a vertical plane extendingl longitudinally of said frame. a pad assembly suspended at the lower-ends of said links. means for reciprocating said pad assembly and said links. and balance weights mounted on said links at a point spaced above the pivotal connection between said'llnks andnsaid frame. the arms o f said links: between said' weights and said pivotal connections being inclined towards each other in a direction longitudinally of said frame.

14. A sanding device comprising a frame. a plurality of links pivoted intermediate their ends at opposite ends of said. frame for movement opposite sides and adiacent the ends of said u in a vertical plane extending longitudinally oi said frame, a pad assembly connected at opposite ends with one end of said links, balance weights mounted on the other end of said links, and means for reciprocating said pad assembly and said links, the arms of said links carrying said balance Weights being inclined to the plane of said pad assembly throughout the extent of their pivotal movement such that the paths of the inertia forces of said Weights intersect at a point intermediate the connections between said pad assembly and said links at opposite ends of said pad assembly.

15. A sanding device comprising a frame, a motor mounted on said frame, a plurality of links pivoted on said frame for pivotal movement in a vertical plane longitudinally of said frame, a sanding plate assembly below said frame, an intermediate member between said sanding plate assembly and said frame, said intermediate member having a driving connection with said sanding plate assembly and having a pivotal connection with the lower end of said links, the portion of said intermediate member providing a driving connection with said sanding plate assembly being resilient in a vertical direction and substantially inflexible in a, direction longitudinally of said frame, and means driven by said motor for reciprocating said intermediate member and sanding plate assembly along a path extending longitudinally of said frame.

16. A sanding device comprising a frame, a motor mounted on said frame, a plurality of links pivoted on said frame adjacent opposite ends of the frame for movement in a vertical plane longitudinally of the frame, a sanding plate assembly below said frame, an intermediate member between said sanding plate assembly and said frame, said intermediate member having a pivotal connection with the lower ends of said links and having a driving connection with said sanding plate assembly, the portion of said intermediate member providing a driving connection with said sanding plate assembly being resilient in a vertical direction and substantially inilexible in a direction longitudinally of the frame, and means driven by said motor for reciprocating said intermediate member along a path extending longitudinally of said frame.

FRANKLIN A. DUBSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,160,452 Sargent Nov. 16, 1915 1,868,507 Roos July 26, 1932 2,113,694 Kehle Apr. 12, 1938 2,193,418 George Mar. 12, 1940 2,205,492 Reid June 25, 1940 2,358,518 Kraft Sept. 17, 1944 2,367,668 Champayne Jan. 23, 1945 2,395,537 Crosby Feb. 26, 1946 FOREIGN PATENTS Number Country Date 357,772 Italy Mar. 26, 1938 

